'Chatty Turtles' Flip the Script on the Evolutionary Origins of Vocalization in Animals

'Chatty Turtles' Flip the Script on the Evolutionary Origins of Vocalization in Animals

Pakinam Amer: This is Scientific American’s 60-Second Science. I’m Pakinam Amer.

Clicks, clucks, grunts, and snorts—these are not sounds that we typically associate with turtles.

[CLIP: Audio of South American juvenile turtles]

Amer: They’re actually thought to be very quiet or even silent. But it looks like we may have grossly underestimated how much sound they can make. Now a new study in Nature Communications has collected vocal recordings from 53 species of turtles and other animals that were otherwise considered to be mute.

[CLIP: Audio of South American juvenile turtles]

Amer: Those clicks you’ve just heard were calls made by baby giant Amazon River turtles swimming together. A group of evolutionary biologists and other scientists in five different countries pored over these recordings and combined them with vocal repertoires of about 1,800  animal species from other studies.

Amer: They were able to piece together evidence that the last common ancestor of all lungfish and tetrapods started vocalizing more than 400 million years ago. (And just in case you aren’t familiar, tetrapods are four-limbed vertebrates that include amphibians, mammals, birds, and reptiles.) That’s at least 100 million years earlier than previous studies had suggested.

Amer: The new revelations amount to a rewriting of the acoustic history of animals with backbones. 

Gabriel Jorgewich-Cohen: I did fieldwork in the Brazilian Amazon with a researcher that published one of these first papers showing that turtles can communicate acoustically, and that inspired me. So I went back home, and I got a piece of equipment, and I started recording my own pets. And I discovered that they were producing sounds as well, and the species I had were not known to produce sounds. So I started thinking maybe they all do, and I went out there, and I recorded as many as I could [laughs].

Amer: That was Gabriel Jorgewich-Cohen, a researcher at the University of Zurich and study co-author. By the way, the pets he’s talking about are Giant Amazon River turtles, more commonly known as red-eared slider turtles in the US.

Jorgewich-Cohen: This is the only species known to have post-hatch parental care among all turtles, which is pretty amazing. And they discovered this by recording the sounds of the animal—not only this species but also sea turtles,[[OR (if uncertain): Jorgewich-Cohen: Sea turtles,]] for example when they are in the nest, the hatchlings start vocalizing from within the egg to synchronize hatch. And also when they come out altogether, they individually have less chance of being eaten by another animal. And in the case of the Amazon River turtle, when they go to the water, the females are there waiting for them, and they are also vocalizing. And they find each other, and then they migrate together up the river to the forest.

Amer: A previous study published in 2020 by researchers at the University of Arizona concluded that only two of 14 families of turtles vocalized. It also stated that acoustic communication evolved independently in most major tetrapod groups, with origins in the range of 100 million to 200 million years ago. But now we know that’s not the case.

Jorgewich-Cohen: I was very surprised—happily surprised—when I found so many different types of sounds. And I kept recording more and more animals. And every animal I recorded made sounds; I had no negative results whatsoever. And that was surprising by itself. 

Amer: Jorgewich-Cohen recorded hundreds of hours’ worth of footage over two years—not just of turtles but also of lungfish, tuatara and other creatures. Animals typically produce sounds for many reasons: to define territory, to attract a mate or to communicate with their young ones. It’s a useful skill. 

Jorgewich-Cohen: I found that for many turtle species, there are sounds that are only made by males, there are some that are only made by females, and some only by juveniles, and some that males will only make when they are in front of the female.

Amer: If there’s one animal from this study that I would’ve sworn is 100 percent mute, it’s the caecilian. For those who’re not familiar, let me paint a little picture: Caecilians are slippery, slimy and slithery little things. They burrow, and they look like earthworms or even snakes. But they’re neither. They’re in fact amphibians. They have a backbone and a skull, jaws and all, but no limbs. And like manytetrapods, they emit sounds through their respiratory tract, just like their common ancestor. It’s actually not very easy to come across one,.

Jorgewich-Cohen: The caecilian was a special one because I definitely expected it not to make any sounds. And it’s not only that it does, but it makes very strange and very loud sounds.

[CLIP: Audio of caecilain]

Amer: Not to be crass, but that sounds a bit like a fart. 

Jorgewich-Cohen: When I heard it for the first time, I started laughing, and I sent it to my friends who did fieldwork with me. They also started laughing, and they said, “I cannot believe you. You made the sound with your mouth, and you’re sending me the file.” I was like, “No, I swear.”

Amer: The study, “Common Evolutionary Origin of Acoustic Communication in Choanate Vertebrates,” is less focused on the function of these sounds, and more on the evolution of acoustic signals. But in future studies, the researchers plan to dig deeper by analyzing the sounds further in an attempt to understand what they mean.

Jorgewich-Cohen: We try to also make footage of the animals while we’re recording the sounds so we could try to correlate any type of behavior to the sound that they were making and try to understand how they use the sounds or what ideas they convey.

Amer: Sometimes Jorgewich-Cohen and his colleagues would find more than 30 different sounds in a single species’ repertoire. It seems that the more socialized the animal is, the more vocally diverse it is, he says. But further studies are needed to confirm this.

Jorgewich-Cohen: Hopefully this is the beginning of a new field of study. So people are going to go out there and try to record more of these animals and get to new conclusions and new discoveries. But it will be really cool if we could, for example, do playback experiments and try to understand if they reply to the sounds we make. And then we can start understanding what these sounds mean and how they are used.

Amer: Thank you for listening! For Scientific American’s 60-Second Science, I’m Pakinam Amer.

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